1. Field of the Invention
The invention relates to an image pick-up apparatus, comprising an image sensor with a plurality of gate electrodes which define light-sensitive elements in a semiconductor body which convert incident radiation into collected charge carriers, and also comprising a control circuit for the gate electrodes. The invention also relates to an X-ray examination apparatus comprising such an image pick-up apparatus.
2. Description of the Related Art
An image pick-up apparatus of this kind is known from United States Patent Specification U.S. Pat. No. 4,926,225. The known image pick-up apparatus comprises an image sensor with light-sensitive elements in a semiconductor body which are separated by gate electrodes, thus forming a so-called charge-coupled device (CCD) image sensor. When light radiation is incident on a photosensitive element, electric charges are released at the area of said element by absorption of light quanta and collected as a charge package with an amount of charge which corresponds to the intensity of the incident light radiation. The photosensitive elements together pick up a light image by conversion into a charge carrier image, the brightness value in a pixel of the light image corresponding to the charge in a corresponding light-sensitive element. The prior-art image pick-up apparatus comprises the control circuit in order to adjust the electric voltage applied to the gate electrodes in conformity with a selected mode of operation of the image pick-up apparatus. The region of a light-sensitive element wherefrom charges are collected extends from the charge collection region of the light-sensitive element in the depth direction of the semiconductor body. The depth of the region wherefrom charge is collected can be influenced by adjustment of the gate voltage. In order to reduce crosstalk between neighboring light-sensitive elements, notably for radiation having a comparatively long wavelength such as, for example infrared light, in a prior-art image pick-up apparatus the depth of the regions of the light-sensitive elements wherefrom charge is collected is reduced as the wavelength of the incident radiation is longer, and hence the penetration depth of the incident radiation is greater. The charge released by deeply penetrating radiation which is incident on a light-sensitive element is thus prevented from being collected in a neighboring light-sensitive element where it would cause crosstalk. Consequently, during operation of the known image pick-up apparatus crosstalk is avoided when incident image-carrying radiation of great penetration depth is picked up. The lateral dimensions of the light-sensitive elements of the described image pick-up apparatus, however, cannot be influenced and the spatial resolution of the described image pick-up apparatus cannot be adapted; moreover, it is not possible to increase the spatial resolution, if desired, other than by replacement of the entire image sensor.